Many different types of contaminants are present in polluted groundwater and soil. The potential for humans or sensitive ecosystems to be exposed to such contaminants is strongly affected by a number of factors. Because speciation controls the environmental transport and risks of these contaminants, it is important to measure not only the contaminant concentration, but also its oxidation state.
Mercury is of particular concern because it is a highly toxic element that is widely disseminated throughout the atmosphere and hydrosphere. Additionally, the toxicity, biochemical behavior, and bioavailability of mercury are strongly dependent on the chemical form of the element. Among the three common forms of mercury: elemental mercury)(Hg0), ionic mercury (He), and organic mercury complexes (methylmercury, ethylmercury, phenylmercury, etc.), methylmercury (CH3Hg2+) is the most toxic and abundant form of mercury found in the environment. Depending on environmental conditions, mercury can also transform among the different forms, so the existence of any form of mercury is potentially harmful to human health.
Natural mercury emissions have led to the distribution of mercury throughout the environment via volcanoes, fires, rivers, and biological processes. Off-gassing of mercury from the lithosphere and hydrosphere to the atmosphere results in the deposition of mercury in aquatic and terrestrial environments.
In addition to natural mercury emissions, industrial activities (e.g. coal mining, silver mining, burning of fossil fuels, and other industrial processes) have created new mercury emission pathways to various sites in the environment. Approximately 80% of anthropogenic mercury emissions release elemental mercury) (Hg0) into the air through industrial processes. Meanwhile, almost 15% of this mercury is released into the terrestrial environment. The final 5% of anthropogenic mercury emissions is transported from industrial wastewater to the aquatic environment. A total estimate of 4,700 tons of mercury is released from human-related activities each year to deposit in the environment. Deposited mercury can then re-emit into the atmosphere by biological and geological means.
Concentrated mercury, especially methylmercury, poses serious problems to human health, as bioaccumulation of mercury within the brain and kidneys ultimately leads to neurological diseases. Therefore, mercury monitoring and mercury speciation are important for the environment and human health.